In industrial measurements technology, especially in automation, and process control, technology, field devices are applied, which, in the course of a process, ascertain process-variables by means of sensors or control control-variables by means of actuators. Such field devices ascertain and/or control, for example, pressure, flow, fill level, temperature or some other physical and/or chemical process variable as a process variable in a process. Available from Endress+Hauser are such field devices, for example, under the marks, CERABAR, DELTABAR, DELTAPILOT, PROMASS, LEVELFLEX, MICROPILOT, PROSONIC, SOLIPHANT, LIQUIPHANT and EASYTEMP. These serve primarily to determine and/or to monitor at least one of the above referenced process variables of a medium in a containment.
A feature common to all the above mentioned measuring, or field, devices is that, from the process variables ascertained by the sensors, a measured value is ascertained and evaluated by means of device electronics connected thereafter. This device electronics is, most often, so matched to the corresponding measuring requirements and the process variable to be measured, that, for each sensor principle, for each process variable to be measured and for each measuring performance, an independent device electronics must be developed. Another solution is e.g. to equip field devices of different measurement accuracy standards with a unified device electronics and with a maximal measuring performance and to activate or to deactivate the individual functionalities e.g. per software. This has, however, the disadvantage, that, by equipping the field device for maximal performance also maximum possible memory capacity must be provided for program and data, and the device electronics must already have all expansion electronics. This is very expensive.
Another possibility is to increase the functionality of a basic, standardized, device electronics by adding expansion electronics. Disadvantageous in the increasing of the functionality of the total field device by such expansion electronics is that the programs of the field device must be overwritten with a new version of an operating program matched to the expansion electronics, i.e. firmware must be overwritten and, also here, maximum memory size must be provided beforehand for the program and the data.
These solutions have the disadvantage that, as soon as the functional scope of a field device is desired to be expanded, the customer or operator has been obliged, to this point in time, either to obtain a completely new field device, or, after the possible plugging in of a new device module, to have new firmware written into the field device. The customer or operator would prefer, in the case of an expansion of the functionality of the field device, in general, not to have to buy a completely new field device, and the manufacturer cannot, for each field device, offer the opportunity to write over the firmware, since this implies, besides pure hardware costs, such as e.g. connectors, galvanically isolated lines, also a not to be disregarded logistical effort in managing the different programs and different device electronics.